The present invention relates to the field of a resistance welder and, more particularly, to a resistance spot welder, in which one gun arm and the other gun arm are rotatably connected through a spindle (as will be called the “shaft”) and in which the power of an actuator is mechanically transmitted to the one gun arm, to rotate the gun arm on the shaft thereby to generate a pressure necessary for the welding operation between a pair of electrode tips supported at the leading ends of the two gun arms, whereby a welding current is fed to plates pressed to be welded between the electrode tips.
In an X-type resistance spot welder (as will be called the “X-Gun”) of the related art including a robot spot welding gun, a portable spot welding gun or a stationary type spot welder, one gun arm is set on the movable side whereas the other gun arm is set on the stationary side, and these gun arms are connected by a spindle rotating device. In the spindle rotating device of this kind, the power of the actuator such as an air cylinder or an electric motor is transmitted to one gun arm so that the gun arm is rotationally driven on the shaft. As a result, a pair of confronting electrode tips, as individually supported by the gun arms, are brought close to or apart from each other.
The spindle connecting device of the X-gun includes the following examples in the related art. In the example (as referred to JP-B-7-63852, page 2, column 3, line 27-column 4, line 7), with a view to adjusting the clearance to be formed by the wear of a thrust washer due to the rotational motion of the shaft thereby to prevent the misalignment of the leading end of an electrode tip, an insulating thrust washer is arranged on the inner side or the outer side of the bifurcation of the gun arms and in alignment with a shaft (or a hinge pin), and a pushing force is applied in a direction substantially normal to the side of the thrust washer to move the thrust washer in the same axial direction as that of the hinge pin so that the clearance formed on the sliding face of the thrust washer is eliminated to prevent the misalignment between the electrode tips to be formed at the leading ends of the gun arms.
In a related spindle connecting device of another example (as referred to JP-UM-B-7-35662, page 2, column 3, line 6-line 15), bearings having flanges (or ring members having an L-shaped longitudinal section) are removably mounted from the two sides in the bearing holes of the support portions of two gun arms, a support pin is inserted into the bearings with the washers and the flanges abutting against the flanged bearings. The support pin has a lubricant passage in its axial direction. The lubricant passage has a thin oil passage communicating therewith in the abutment faces between the washers and the flanges. The bearings and the washers are fastened and fixed between the brackets.
As another example, there is a related spindle connecting device (as referred to-JP-UM-B-7-50062, page 2, column 3, line 6-line 15), in which the shaft is inserted in the hinge portion of the two gun arms to connect them rotatably. Between the hinge portions connected, an electric insulating having a wear-resisting material applied to the annular surface is fixed by a stopper pin, whereby the connecting portion of the hinge portions is reliably insulated to reduce the wear of the hinge portions.
As another example, there is an related X-gun (as referred to JP-A-2005-28454, [0012]-[0022]), in which a shaft (or a pin) is inserted into bearing holes of two intermediate arms, one of which is connected rotatably on the shaft. Gun arms are inserted and fixed in insulating bushings attached to the intermediate arms. The gun arms and the intermediate arms are electrically insulated. Gun brackets are connected to the shaft at the center, and a welding transformer is fixed to the extensions of the gun arms. To an action fork having two symmetric plates connected on the common axis to the shaft and arranged in parallel, there are connected the intermediate arm supporting one gun arm and a cylinder body for establishing a pressing stress necessary for rotating on the shaft at the intermediate arm for supporting the other gun arm, so that the weight of the X-gun with the welding transformer is reduced.
As another example, there is a related welding gun (as referred to JP-A-2005-169507, [0006]-[0011]), in which one gun arm is rotatably connected on a moving side to a gun bracket through the spindle connecting device, and in which the other gun arm is integrally connected and fixed as a fixed side to the leading end of the gun bracket, so that an electrode tip on the stationary side is brought, prior to the electrode tip on the moving side, by the control on the robot side into contact with a workpiece.
The related are disclosed in JP-B-7-63852 needs not only the insulating washer for arranging the washer to insulate the gun arms on the inner side and the outer side of the bifurcation of the gun arms, on the same axis as that of the shaft but also the fixing means, so that the number of parts is accordingly increased to enlarge the structure.
The related art disclosed in JP-B-UM-7-35662 needs the oil passage formed in the abutment face between the washer and the flange portion and branched from the lubricating oil passage formed in the axial direction of the shaft, so that the structure of the spindle connecting device is accordingly complicated to require a large step number for the manufacture.
In the related art disclosed in JP-B-UM-7-50062, the electric insulator is positioned and fixed at the connecting hinge of the two gun arms by the positioning and rotation-stopping pins, and the wear-resisting annular plate is adhered to the mutually sliding faces of the electric insulator, so that the structure of the spindle connecting device is accordingly complicated.
The related art disclosed in JP-A-2005-28454 does not need the electric insulation at the shaft of the spindle connecting device in that the gun arms are inserted and fixed through the insulating bushings in the two intermediate arms rotatably connected by the spindle connecting device. The gun brackets, the plates supporting the actuator and the intermediate arm are connected on a common axis by the spindle connecting device. Thus, the axial length of the shaft is enlarged, and the plates are needed in addition to the gun bracket, so that the number of parts and the number of manufacturing steps are accordingly increased. Moreover, no consideration is disclosed into the oilless spindle connecting device (or the oilless spindle) and the cooling device.
In the related art disclosed in JP-A-2005-169507, the stationary side arm and the gun bracket are integrated. However, the spindle connecting device discloses the constitution of the spindle connecting device of the X-gun, but fails to simplify and lighten the spindle connecting device needing no insulation of the shaft.
The X-gun of the related art mostly needs the electric insulation at the shaft so that the spindle connecting device is complicated to a large size. Moreover, the gun brackets or the gun arms are individually assembled as single parts having independent functions, and the design has to be changed, each time the shape and size of the panel work are varied, thereby to raise a cause for a cost increase. In the spindle connecting device of the related art, moreover, the lubricant is fed from the shift inside to the sliding faces. As a result, it is difficult to make an oilless structure for clearing the calculated lifetime on the design of the shaft. Moreover, the X-gun of the related art has found it difficult to make compact the wiring structures of the secondary circuit of such a welding unit and the cooling circuit as includes the secondary conductor and/or the shut connected from the welding transformer to the electrode tips. Moreover, the X-gun of the related art has failed to solve the problem that only the gun arms are exclusively replaced according to the variation of the shape of a weld workpiece.